1. Field of the Invention
This invention relates to a control system for internal combustion engines, and more particularly to an control system for an internal combustion engine adapted to perform control of a fuel injection amount while taking into account an amount of fuel (liquid fuel) adhering to the inner wall surface of the intake pipe of the engine after being injected into the intake pipe.
2. Prior Art
In an internal combustion engine wherein liquid fuel such as gasoline is injected into the intake pipe of the engine, part of the injected fuel adheres to the inner wall surface of the intake pipe so that unfavorably a required amount of fuel is not supplied to the combustion chamber of the engine. A fuel supply amount control method for internal combustion engines, which eliminates the above inconvenience, has been known, for example, from Japanese Provisional Patent Publication (Kokai) No. 61-126337, which estimates an amount of fuel (adherent fuel amount) adhering to the inner wall surface of the intake pipe and a fuel amount carried off (drawn) from the inner surface of the intake pipe into the combustion chamber of the engine due to evaporation of adherent fuel or a drawing force of intake air, to determine the fuel injection amount for the engine by taking into account these estimations. That is, the method corrects an amount of fuel to be injected into the engine determined based on operating conditions of the engine, according to these estimated values of the adherent fuel amount and the carried-off fuel amount.
However, in the conventional method of the adherent fuel-dependent correction does not contemplate the fuel injection timing, which can result in an excessive correction of the fuel injection amount and hence failure to achieve satisfactorily excellent fuel consumption and exhaust emission characteristics. Especially, in a transient operating condition of the engine, the method fails to effect proper correction of the fuel injection amount to make the air-fuel ratio of a mixture supplied to the engine difficult to be converged, which results in degraded drivability.